A wide variety of friction sheet feeding machines are available for feeding individual sheets from the bottom of an essentially vertical stack of sheets. These machines typically include (i) a tray for holding a stack of sheets in an essentially vertical position, (ii) a nip for feeding a lowermost sheet from the stack, (iii) a driven friction roller or belt for contacting the downward facing major surface of the lowermost sheet in the stack and pulling the lowermost sheet from underneath the sheet stack towards the nip, and (iv) a friction retard surface positioned above the driven friction roller for contacting the leading edge(s) and any exposed upward facing major surface(s) of the sheet(s) positioned directly above the lowermost sheet for retarding advancement of the sheet(s) directly above the lowermost sheet and thereby facilitating separation of the lowermost sheet from the immediately overlying sheet prior to introduction of the lowermost sheet into the feed nip.
Friction retard surfaces having a wide variety of sizes, shapes, contours, coefficient of friction, etc., have been employed over the years. Rotating friction retard rollers have also been employed, with the retard roller rotated in a forward direction on some machines and rotated in a reverse direction on others. While a forward rotating friction retard roller provides significant advantages when feeding certain types of sheets, such as coarse flat product, and a reverse rotating friction retard roller provides significant advantages when feeding other types of sheets, such as coated, glossy, printed product, the direction of rotation limits the types of sheets which may be reliably fed through the friction sheet feeding machine.
Accordingly, a need exists for a friction sheet feeding machine capable of providing the advantages associated with a rotating friction retard roller without the limitations also associated with a rotating friction retard roller.